So, here's the story: I was flying CPT-JNB on a Kulula (Boeing 738) flight. It was a late evening flight (so possibly the last flight of the day for the aircraft) and after we landed at JNB and pulled into the gate, we sat there for a good five minutes with the engines running before they were shut down and we were allowed to disembark.

I assume that the five minutes of idling is to allow the engines to reach some kind of equilibrium before they're shut down for the night -- would that be a correct assumption? I've never experienced this before -- the majority of the time when I've been on an arriving aircraft, the engines have been shut down pretty soon after stopping at the gate, so I'm curious what would be different this time.

Possibly waiting for ground power if the APU was inop?

Adispatcher wrote:

Possibly waiting for ground power if the APU was inop?

That would be my guess as well. Our NG's have a recommended 3 minute cool down after landing (and the MAX is mandatory) but this sounds like it was something else.

barney captain wrote:

Adispatcher wrote:

Possibly waiting for ground power if the APU was inop?

That would be my guess as well. Our NG's have a recommended 3 minute cool down after landing (and the MAX is mandatory) but this sounds like it was something else.

At the time I wondered if the APU was playing up ... I'd forgotten about that. Of course unless the actual pilot gets on here and tells us, we'll never know -- it's only guesswork (and completely uneducated guesswork on my part!)

BreninTW wrote:

barney captain wrote:

Adispatcher wrote:

Possibly waiting for ground power if the APU was inop?

That would be my guess as well. Our NG's have a recommended 3 minute cool down after landing (and the MAX is mandatory) but this sounds like it was something else.

At the time I wondered if the APU was playing up ... I'd forgotten about that. Of course unless the actual pilot gets on here and tells us, we'll never know -- it's only guesswork (and completely uneducated guesswork on my part!)

If the aircraft was dispatched with the APU inop, they would have would have had to do a Copco start in CPT which takes longer than normal, did you notice anything different on start up? Otherwise the APU might not have started on landing.

Balerit wrote:

If the aircraft was dispatched with the APU inop, they would have would have had to do a Copco start in CPT which takes longer than normal, did you notice anything different on start up? Otherwise the APU might not have started on landing.

No, I didn't notice anything unusual on start up -- but it's unlikely I would. The 737 family is not an aircraft I fly with any kind of regularity. This year was the first time I've been on a 737 in at least five years.

Assuming the runway didn't literally end at the gate, the aircraft would - under most circumstances - have spent enough time taxying to meet the required cool-down period.

Chances are the aircraft arrived at gate before the ground crew, and was waiting for a GPU. In those cases you can either light up the APU or wait for the GPU with one or more engines running. If you chose the former, chances are ground crew will appear within seconds of starting the APU. If you chose the latter, thinking (or having been told) ground crew are 'just around the corner', chances are they'll be late and you'll be sat there with a donk running for a few minutes. It's the Murphy's Law of Ground Handling

I just leave an engine running to keep the rampers from popping the cargo door and blocking me in while I wait for the gate agent to maneuver the jetbridge and finally open the passenger door. The most extreme example was waiting 15 minutes for the jetbridge and the rampers had already unloaded all of the cargo compartments and a plane-full of unhappy passengers standing in the aisle waiting for the door to open.

I've disembarked a plane with the engine running.

Not unusual to leave #4 on an L-188 at idle, back in the day.
Rampers knew to keep a good distance. You didn't have to get very close to hear and feel the power of that propulsion system.

CFM-56 will used the starting motor to doing the engine to prevent differential cooling binding the bearings (The PW1100G issue). Are we Shure this isn't what we're seeing? This will go for up to 45 minutes in a CFM-56 and up to 75 minutes in the PW1100G.

The downside is that it teaches ground crew to ignore spinning engines...

Lightsaber

One of the pilots told me that should they have to hold anywhere while taxing in and then have to take power to carry on, then they have to idle 3 minutes after that for cooling the CFM engines, so if they had to hold before crossing 03L to get to the apron then they would have to idle for 3 minutes because it's about a hundred metres to the bays.

CFM-56 will used the starting motor to doing the engine to prevent differential cooling binding the bearings (The PW1100G issue). Are we Shure this isn't what we're seeing? This will go for up to 45 minutes in a CFM-56 and up to 75 minutes in the PW1100G.

Lightsaber, 99pc of what you post is good gen, but this is just rubbish. Starter motors have time limits because they are not cooled very well. The usual maximum is 5 minutes, followed by 45 minutes OFF before next use.
You cannot use a starter motor to spin an engine for longer than 5 mins.
When I used to do boroscopes, I used to motor the engine for 5 minutes to cool it down before climbing in, but never longer.

The modern health and safety rules in Europe are that, if an engine is running the beacons are on. If the beacons are on the ramp staff do not cross the line into the gate area. This can be modified with an inop APU, but only after radio contact with the crew. If the beacons are on, the jetty coes not move towards the aircraft.. This can create a standoff at times with the ramp waiting for the engines to stop, and the aircrew waiting for ground power, but that is what H and S rules have produced. I have seen ASR s raised by the aircrew when the ground power is plugged in before the beacons are off. The aircrew are taught to shut the aircraft down if ground power is not available, and sit on battery power until it arrives. Not pleasant for the passengers, but if a ramper is hurt by a running engine, the airport manager can go to prison!!!!

Tristarsteve wrote:

CFM-56 will used the starting motor to doing the engine to prevent differential cooling binding the bearings (The PW1100G issue). Are we Shure this isn't what we're seeing? This will go for up to 45 minutes in a CFM-56 and up to 75 minutes in the PW1100G.

Lightsaber, 99pc of what you post is good gen, but this is just rubbish.

I meant to respond to this as well but forgot. Yes 5 minutes is max duty cycle as it is the oil that is the limiting factor.

Balerit wrote:

Tristarsteve wrote:

CFM-56 will used the starting motor to doing the engine to prevent differential cooling binding the bearings (The PW1100G issue). Are we Shure this isn't what we're seeing? This will go for up to 45 minutes in a CFM-56 and up to 75 minutes in the PW1100G.

Lightsaber, 99pc of what you post is good gen, but this is just rubbish.

I meant to respond to this as well but forgot. Yes 5 minutes is max duty cycle as it is the oil that is the limiting factor.

Then I'm wrong on how they are spun. Ut there is a way to slowly turn the high spool to prevent differential cooling.

You either let the engines idle for 3-5 minutes or you may dry motor the engine for 5 minutes max using the starter till the EGT is below a certain amount - maybe someone can give us the latest data. Not sure what the very latest engines limits are.

You guys are a ways off on the 737NG starter limits. You can run the starter for two fifteen minute periods with a minimum of two minutes between each starter operation. After that you are limited to running for five minutes with a ten minute wait time. If any starter operation times are exceeded, the starter is unserviceable.

Sorry, I was going from the A318 CFM56 starter.
That has 4 starts of 2 min each with 20secs wait, then 15 minute wait.

Assumed the NG would have a similar starter. Sounds like it has at least double the size of oil cooling.

On the V2500 we have 3 starts of 2min with 15secs between, followed by 30 min cooling.

Perhaps NG engines take much longer to start??

The 737NG normal engine start limits are unlimited starts of 2 min each with 10 sec wait between starts.

The starter is supplied oil from the engine thru the accessory gearbox.

My guesstimate is 30-45 sec to start.

yeelep wrote:

The 737NG normal engine start limits are unlimited starts of 2 min each with 10 sec wait between starts.

The starter is supplied oil from the engine thru the accessory gearbox.

My guesstimate is 30-45 sec to start.

Ah, thanks for the info.